Suction air is required for a multitude of work processes in textile machines. For example, in spinning machines the yarn end is detached by means of suction air from the winding bobbin after a yarn break and is pneumatically prepared for piecing. In winding machines, which have a plurality of winding stations arranged next to each other, a catch nozzle is disposed in the yarn path at each winding station in order to aspirate and hold the leading yarn end of the lower feed yarn, so that no drum winding occurs. Continuously applied suction air in the vicinity of the unwinding bobbin is used to aspirate off dirt, flying dust and fibers being created when the yarn is unwound from the bobbin. Since suction air is always needed for these purposes, the vacuum needed for these purposes is considered the basic or minimum demand for vacuum of the winding machine. Occurrences which produce an increased suction air demand and therefore an increased vacuum requirement are the aspiration of the yarn end prior to piecing the yarn.
As a rule, a suction output is made available for the basic demands or for the work demands, which provides a vacuum which in each case is considered to be optimal on the basis of experimental values. Whether the vacuum provided is actually optimal can only be checked if there is a possibility of making comparisons. It is possible that an initially set vacuum can be reduced without the quality of the yarn suffering or without an increase in defects or a reduction of the efficiency of the machine. On the other hand, it is also possible that the initially set vacuum is not optimal and that the number of occurring errors can be reduced by raising it to a higher level. Thus, an increase in the vacuum results in a further reduction of the absolute pressure, and reducing the vacuum results in an increase of the absolute pressure.
It is known from German Patent Publications DE 44 46 379 A1 and DE 195 11 960 A1 to first set a vacuum at a textile machine, by means of which the basic demands for a vacuum at a textile machine can be met. If the above-mentioned occurrences arise, the vacuum is initially raised to a corresponding level to assure that the occurrences causing an increased vacuum demand can be addressed, while the basic demands of the machine are satisfied at the same time.
From German Patent Publication DE 195 11 960 A1 it is furthermore known to check the quality of the work performed in connection with the processing of occurrences which create a vacuum demand and, in case of deviations from a predetermined tolerance range, to immediately adapt a predeterminable increased vacuum accordingly. This procedure requires an immediate checking of the results of work operations following the occurrence. A resultant correction takes place in relation to the respective occurrence. This results in continuous fluctuations of the vacuum changes provided per occurrence, which are work station-dependent. A transfer to other work stations will possibly result in additional errors.